By Terry Hughes, Barry Hart and Karen Hussey

The Great Barrier Reef has already been badly damaged by global warming during three extreme heatwaves, in 1998, 2002 and 2016. A new bleaching event is under way now.

As shown in a study published in Nature today, climate change is not some distant future threat. It has already degraded large tracts of the Great Barrier Reef over the past two decades.

The extreme marine heatwave in 2016 killed two-thirds of the corals along a 700km stretch of the northern Great Barrier Reef, from Port Douglas to Papua New Guinea. It was a game-changer for the reef and for how we manage it.

Bleaching caused by extreme heat in summer 2016, based on extensive aerial surveys. Category 4 in red: 60-100% of colonies were bleached; Category 3 in orange: 30-60% bleached. Author provided

Our study shows that we cannot climate-proof coral reefs by improving water quality or reducing fishing pressure. Reefs in clear water were damaged as much as muddy ones, and the hot water didn’t stop at the boundaries of no-fishing zones. There is nowhere to hide from global warming. The process of replacement of dead corals in the northern third of the reef will take at least 10-15 years for the fastest-growing species.

The Great Barrier Reef is internationally recognised as a World Heritage Area. In 2015 UNESCO, the world body with oversight of World Heritage Areas, considered listing the reef as a site “in danger” in light of declines in its health.

Australia’s response falling short

In response to concerns from UNESCO, Australia devised a plan, called the Reef 2050 Long-term Sustainability Plan. Its ultimate goal is to improve the “Outstanding Universal Value” of the reef: the attributes of the Great Barrier Reef that led to its inscription as a World Heritage Area in 1981.

We have written an independent analysis, delivered to UNESCO, which concludes that to date the implementation of the plan is far too slow and has not been adequately funded to prevent further degradation and loss of the reef’s values. A major shortcoming of the plan is that it virtually ignores the greatest current impact on the Great Barrier Reef: human-caused climate change.

The unprecedented loss of corals in 2016 has substantially diminished the condition of the World Heritage Area, reducing its biodiversity and aesthetic values. Key ecological processes are under threat, such as providing habitat, calcification (the formation of corals’ reef-building stony skeletons) and predation (creatures eating and being eaten by corals). Global warming means that Australia’s aim of ensuring the Great Barrier Reef’s values improve every decade between now and 2050 is no longer attainable for at least the next two decades.

What needs to change

Our report makes 27 recommendations for getting the Reef 2050 Plan back on track. The following are critical:

• Address climate change and reduce emissions, both nationally and globally. The current lack of action on climate is a major policy failure for the Great Barrier Reef. Local action on water quality (the focus of the Reef 2050 Plan) does not prevent bleaching, or “buy time” for future action on emissions. Importantly, though, it does contribute to the recovery of coral reefs after major bleaching.

• Reduce run-off of sediment, nutrients and pollutants from our towns and farms. To date the progress towards achieving the water quality targets and uptake of best management practice by farmers is very poor. Improving water quality can help recovery of corals, even if it doesn’t prevent mortality during extreme heatwaves.

• Provide adequate funding for reaching net zero carbon emissions, for achieving the Reef 2050 Plan targets for improved water quality, and limiting other direct pressures on the reef.

At this stage, we do not recommend that the reef be listed as “in danger”. But if we see more die-backs of corals in the next few years, little if any action on emissions and inadequate progress on water quality, then an “in danger” listing in 2020, when UNESCO will reconsider the Great Barrier Reef’s status, seems inevitable.

This article was co-authored by Diane Tarte, co-director of Marine Ecosystem Policy Advisors Pty Ltd. She was a co-author of the independent report to UNESCO on the Great Barrier Reef.

Terry Hughes, Distinguished Professor, James Cook University, James Cook University; Barry Hart, Emeritus Professor Water Science, Monash University, and Karen Hussey, Deputy Director, Global Change Institute, The University of Queensland

This article was originally published on The Conversation.